Scintillator panel, radiation image sensor and methods of producing them

ABSTRACT

Scintillator panel ( 1 ) comprises a radiation transmitting substrate ( 5 ), which has heat resistance, a dielectric multilayer film mirror ( 6 ), as a light reflecting film and is formed on the radiation transmitting substrate ( 5 ), and a scintillator ( 10 ), disposed on the dielectric multilayer film mirror ( 6 ) and emits light by conversion of the radiation ( 30 ) that has been made to enter the radiation transmitting substrate ( 5 ) and has passed through the dielectric multilayer film mirror ( 6 ). Since the radiation transmitting substrate ( 5 ) has heat resistance, the dielectric multilayer film mirror ( 6 ) can be vapor deposited at a high temperature and, as a result, can be formed in a state of high reflectance. Also, unlike a metal film, the dielectric multilayer film mirror ( 6 ) will not corrode upon reacting with the scintillator ( 10 ).

TECHNICAL FIELD

This invention relates to a scintillator panel to be used for radiationimaging for medical use, etc., a radiation image sensor that makes useof this scintillator panel, and methods for making these items.

BACKGROUND ART

Radiation image sensors, which convert radiation into electrical signalsand enable electrical processing of the signals, are used widely inmedical and industrial fields. The acquired electrical signals can beprocessed electrically and displayed on a monitor. A representativeexample of such a radiation image sensor is a radiation image sensorthat uses a scintillator material for converting radiation in to light.With this type of radiation image sensor, an image pickup device, forfurther conversion of the converted light into electrical signals, isused in combination. For example, a MOS type image sensor, etc., is usedas the image pickup device. For use in medical fields andnon-destructive inspections (especially inspections using amicro-focused X-ray source, etc.), the irradiation dose of radiation islimited, and thus a radiation image sensor of high sensitivity thatenables a high optical output with the limited irradiation dose isdesired.

FIG. 9 is a longitudinal sectional view of a radiation image sensordescribed in International Patent Publication No. WO99/66345 (referredto hereinafter as “Prior Art 1”). To form this radiation image sensor 4,a scintillator panel 8, comprising a substrate 50, a light reflectingfilm 60, formed on the substrate 50, and a scintillator 10, formed onthe light reflecting film 60, is combined with an image pickup device20, which is disposed so as to face the scintillator 10. Radiation 30enters from the substrate 50 side, passes through the light reflectingfilm 60, and is converted into light at the scintillator 10. The lightresulting from conversion is received by the image pickup device 20 andconverted into electrical signals. The light reflecting film 60 has afunction of reflecting the light emitted by the scintillator 10 andreturning this light to the scintillator 10 side to thereby increase theamount of light entering the light receiving part of the image pickupdevice 20. A film of metal, such as aluminum, etc., is mainly used asthe light reflecting film 60.

FIG. 10 is a longitudinal sectional view of a radiation imaging devicedescribed in JP 5-196742A (referred to hereinafter as “Prior Art 2”).This radiation imaging device 3 comprises a substrate 51, a lightdetector 21, which is disposed on the substrate 51 and serves as animage pickup device, a scintillator 10, formed on the light detector 21,a thin film 41, disposed on the scintillator 10, a light reflecting film70, formed on the thin film 41, and a moisture sealing layer 42, formedon the light reflecting film 70. This arrangement differs largely fromthat of the Prior Art 1 in that the light detector 21 is used as a basemember for fixing and supporting the scintillator 10 and the lightreflecting film 70 is formed above the scintillator 10 across the thinfilm 41. The thin film 41 is formed of an organic or inorganic materialand absorbs the non-uniformity on the scintillator 10 to make the lightreflecting film 70 uniform in reflectance. This publication indicatesthat a dielectric multilayer film, arranged from TiO₂ and SiO₂, etc.,which differ mutually in optical refractive index, may be used as thelight reflecting film 70.

DISCLOSURE OF THE INVENTION

These prior-art radiation image sensors has the following problems. Thatis, with the Prior Art 1, though a metal film is used as the lightreflecting film 60, in many cases, this metal film 60 reacts with thescintillator 10 and undergoes corrosion. Such corrosion becomessignificant especially in a case where CsI (T1) is used as thescintillator 10.

With the Prior Art 2, a dielectric multilayer film is used as lightreflecting film 70, and since the scintillator 10 has a structurewherein a plurality of microscopic, columnar crystals, each with adiameter of approximately several μm to several dozen μm, are arrangedin the form of bristles and thus has minute unevenness on the surface,it is difficult to directly form the dielectric multilayer 70 on such anuneven surface. The thin film 41 is thus interposed to flatten thisunevenness. In order to form the dielectric multilayer film 70 to astate in which it is provided with a high reflectance, vapor depositionmust be performed upon heating the base on which the multilayer film isto be formed to approximately 300° C. However, it is difficult to evensimply apply a high temperature in a case where the thin film 41 is anorganic film. Though it is possible to form a multilayer film at atemperature of no more than 300° C., it is difficult to control thethickness of the film that is formed and the problem that the dielectricmultilayer film 70 becomes formed in a colored state occurs, causing thereflectance to drop and the optical output to decrease. In a case wherethe thin film 41 is formed of an inorganic film, it is difficult to forma flat surface for forming the multilayer film on the scintillator withan inorganic film, and as a result, the dielectric multilayer filmbecomes uneven on the surface (reflecting surface) and cannot beprovided with high reflectance.

Thus an object of this invention is to provide a scintillator panel anda radiation image sensor, which a excellent in corrosion resistance andyet can provide a high optical output, and methods for making such ascintillator panel and radiation image sensor.

In order to achieve the above object, a scintillator panel according tothe present invention is characterized in comprising: a heat-resistantsubstrate; a dielectric multilayer film mirror, deposited on theheat-resistant substrate; a scintillator, deposited so as to arrange aplurality of columnar structures on the dielectric multilayer filmmirror and converting incident radiation into light; and a protectivefilm, covering at least the scintillator; and wherein the dielectricmultilayer film mirror reflects light emitted from the scintillator andreturns this light toward the scintillator.

Since the dielectric multilayer film mirror is formed on theheat-resistant substrate, it is not necessary to form a thin film etc.for making the reflectance uniform in a case where the dielectricmultilayer film mirror is formed on the scintillator, such as a filmthat absorbs the non-uniformity on the scintillator. And since thesubstrate is heat resistant, vapor deposition at a high temperature canbe performed to enable the forming of a dielectric multilayer filmmirror of high reflectance.

Furthermore, the substrate may be a radiation transmitting substrate andthe scintillator may emit light by conversion of the radiation that haspassed through the dielectric multilayer film mirror. In this case, thescintillator preferably has CsI or NaI as the main component. Thescintillator may also be photostimulable phosphor.

The protective film is preferably an organic film. In this case, theprotective film does not need to be formed at a high temperature andthus is readily formable.

As the dielectric multilayer film mirror, a multilayer film havinglaminated structure with alternating TiO₂ or Ta₂O₅ and SiO₂ layers ispreferably adopted. This is because in the case of TiO₂ or Ta₂O₅ andSiO₂, corrosion upon reaction with the scintillator, which occurs with ametal reflecting film, will not occur and good reflectioncharacteristics can be obtained over a wide wavelength range.

A separation preventing layer, which prevents the separation of thescintillator from the dielectric multilayer film mirror, is preferablydisposed between the dielectric multilayer film mirror and thescintillator. The separation preventing layer may be a polyimide layer.

A radiation image sensor according to the present invention comprises:the above-described scintillator panel; and an image pickup device,disposed so as to face the scintillator panel and converting the lightemitted by the scintillator to electrical signals. A radiation imagesensor provided with a scintillator panel of good corrosion resistanceand high reflectance, can thus be realized to enable the light emittedby this scintillator panel to be processed electrically and displayed ona monitor, etc.

Furthermore, by providing a light-absorbing housing that covers thescintillator panel, the generation of stray light due to scattering ofthe light that has passed through the dielectric multilayer film mirrorand the generation of noise due to the entry of extraneous light can berestrained to enable to a high S/N ratio and high resolution to beachieved. This housing is preferably made of polycarbonate and its innersurface is preferably matte furnished.

Furthermore, putting the scintillator panel into adhesion with the imagepickup device by means of fixing jigs is even more preferable as thiswill restrain the leakage of light and the occurrence of cross-talk.

A method of making a scintillator panel according to the presentinvention comprises the steps of: preparing a heat-resistant substrate;repeatedly depositing a dielectric film of desired thickness onto thesubstrate to form a dielectric multilayer film mirror with predeterminedreflection characteristics; depositing columnar structures of ascintillator on the dielectric multilayer film mirror; and coating thescintillator with a protective film.

A method for making a radiation image sensor according to the presentinvention further comprises a step of positioning an image pickup deviceso as to face the scintillator manufactured by the abovementioned steps.A step of covering the scintillator panel with a light-absorbing housingmay also be provided.

The scintillator panel and radiation image sensor according to thepresent invention can be made favorably by these making methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a first embodiment of ascintillator panel according to the present invention.

FIG. 2A to FIG. 2F are diagrams for explaining the steps for making thescintillator panel of FIG. 1.

FIG. 3 is a longitudinal sectional view of a first embodiment of aradiation image sensor according to the present invention.

FIG. 4 is an enlarged sectional view for explaining the operation of theradiation image sensor of FIG. 3.

FIG. 5 and FIG. 6 are longitudinal sectional views for explaining asecond embodiment of a scintillator panel according to the presentinvention.

FIG. 7 and FIG. 8 are longitudinal sectional views for explaining secondand third embodiments of a radiation image sensor according to thepresent invention.

FIG. 9 and FIG. 10 are longitudinal sectional views of prior-art typeradiation image sensors.

BEST MODES FOR CARRYING OUT THE INVENTION

Favorable embodiments of this invention shall now be described in detailwith reference to the attached drawings. To facilitate the comprehensionof the explanation, the same referring numerals denote the same parts,where possible, throughout the drawings, and a repeated explanation willbe omitted.

FIG. 1 is a longitudinal sectional view of a first embodiment of ascintillator panel according to the present invention. The scintillatorpanel 1 comprises a Pyrex glass substrate 5 as a radiation transmittingsubstrate with heat resistance, a dielectric multilayer film mirror 6,formed on the Pyrex glass substrate 5, a polyimide layer 7, formed onthe dielectric multilayer film mirror 6 as a separation preventinglayer, and a scintillator 10, formed on the polyimide layer 7 andemitting light converted from the radiation 30 that has entered thePyrex glass substrate 5 and has passed through the dielectric multilayerfilm mirror 6 and the separation preventing layer 7. The scintillator 10has a structure wherein a plurality of microscopic columnar crystals,each with a diameter of a few μm to a few dozen μm, are arranged in thefrom of bristles. The entirety of these is covered by a polyparaxlylenefilm 12 as a protective film. A thin film of SiN, etc., may be providedbetween the Pyrex glass substrate 5 and the dielectric multilayer filmmirror 6. This thin layer is useful to make the glass substrate surfacea uniform, clean surface. As the dielectric multilayer film mirror 6,for example a multilayer film, wherein TiO₂ and SiO₂, which differmutually in optical refractive index, are alternately laminatedrepeatedly a plurality of times, is used, and this film mirror acts as alight reflecting film that reflects and amplifies the light emitted bythe scintillator 10. T1-doped CsI is used for example for thescintillator 10.

When a scintillator, having a structure wherein a plurality of columnarcrystals are arranged in the form of bristles, is to be formed, a basemember that fixes and supports the scintillator is necessary, in thepresent embodiment, the Pyrex glass substrate 5 is used as the basemember that fixes and supports the scintillator 10. Though it ispossible to form the scintillator 10 using an image pickup device as thebase member, in this case, the image pickup device will be subject toheat repeatedly in the process of forming the scintillator 10 as well asin the process of forming the dielectric multilayer film mirror 6 andcan thus become damaged. According to the present embodiment, since thescintillator 10 is formed on the Pyrex glass substrate 5, such a problemis resolved. Also, since this Pyrex glass substrate 5 is heat resistant,vapor deposition at a high temperature close to 300° C. is enabled andthis enables the dielectric multilayer film mirror 6 to be formed to astate wherein it has a high reflectance.

Also, the dielectric multilayer film is excellent in corrosionresistance and thus will not corrode upon reacting with the scintillator10 as in the case of a metal film. The corrosion in the case of a metalfilm is considered to corrosion of the metal film by T1 in the CsI withthe moisture ingress into the interior of the scintillator panel andthis required devising a structure for preventing the moisture ingressinto the panel interior. However, according to the present embodiment,this requirement is eliminated by the use of the dielectric multilayerfilm mirror 6 of high corrosion resistance.

Furthermore, since the polyimide layer 7 is provided as a separationpreventing layer between the dielectric multilayer film mirror 6 and thescintillator 10, the separation of the scintillator 10 from thedielectric multilayer film 6, which may occur when the thickness of thescintillator 10 is increased (especially to 400 μm or more), isprevented.

The steps for making this scintillator panel 1 shall now be described.First, as the radiation transmitting substrate 5, a Pyrex glasssubstrate 5 of 20 cm square and 0.5 mm thickness is prepared (see FIG.2A), and TiO₂ 6₁, 6₃, . . . 6₄₁ and SiO₂ 6₂, 6₄, . . . 6₄₂ are laminatedalternately and repeatedly onto this Pyrex substrate 5 by vacuum vapordeposition (see FIG. 2B and FIG. 2C) to form a dielectric multilayerfilm mirror 6 comprising a total of 42 layers (total thickness:approximately 4 μm) (see FIG. 2D). By controlling the film thickness ofeach layer, a predetermined reflectance for a predetermined wavelengthrange can be secured for the dielectric multilayer film mirror 6 as awhole.

As the radiation transmitting substrate 5, besides a Pyrex glasssubstrate, an amorphous carbon plate or an aluminum plate may be used.In the case of an aluminum plate, the dielectric multilayer film mirror6 is formed after performing sandblasting using glass beads (#1500) toremove rolling scars on the aluminum surface. On the dielectricmultilayer film mirror 6, a highly transparent polyimide layer (forexample, type name RN-812, made by Nissan Chemical Industries, Ltd.), asa separation preventing layer 7, is cured and then coated to a filmthickness of 1 μm by spin coating (see FIG. 2E). Thereafter, columnarcrystals of CsI of a thickness of 300 μm are formed by vapor depositionas a scintillator 10 on the polyimide layer 7 (see FIG. 2F). Then inorder to flatten foreign matter and anomalous growth parts on the CsIsurface, a glass plate is placed on the CsI surface and pressure isapplied at a force of 1 atmosphere. Lastly, a polyparaxylylene film 12of 10 μm thickness is formed by CVD as a protective film that covers theentirety, and the scintillator panel 1 shown in FIG. 1 is thus formed.

In a case where a scintillator panel 1 with a large area of 30 cm squareor more is to be formed, the polyimide layer 7 is formed to a thicknessof 1 μm and screen printing is used as the coating method. Also in orderto improve the luminance in accompaniment with the increased size, thescintillator 10 is made 500 μm in the thickness.

FIG. 3 is a longitudinal sectional view of a radiation image sensor 2according to the present invention. This radiation image sensor 2 isarranged by combining an image pickup device 20 with the scintillator 10of the scintillator panel 1 shown in FIG. 1 by positioning the imagepickup device 20 so as to face the scintillator 10. The image pickupdevice 20 converts the light emitted by the scintillator 10 intoelectrical signals. For example, a MOS type image sensor havingtwo-dimensionally aligned Si photodiodes is used as the image pickupdevice 20.

FIG. 4 is an enlarged sectional view for explaining the operation of theradiation image sensor 2. Radiation 30, which has not been blocked by orhas been transmitted through a subject 32, passes through thepolyparaxylylene film 12, Pyrex glass substrate 5, dielectric multilayerfilm mirror 6, and polyimide layer 7 and enters the scintillator 10. Thescintillator 10 converts the incident radiation 30 into light and emitsthis light. Part of the light emitted from the scintillator 10 proceedstowards the dielectric multilayer film mirror 6 and this light isreflected by the dielectric multilayer film mirror 6 and is returned tothe scintillator 10. Most of the light that is emitted is thus directedtowards and received by the image pickup device 20. The image pickupdevice 20 converts the received light image information into electricalsignals and outputs these signals. The electrical signals that are thusoutput are sent to and displayed on a monitor, etc., as image signals,and since the image here is one resulting from the conversion of aradiation image that entered the radiation image sensor 2 into a lightimage by the scintillator 10 and further conversion into electricalimage signals by the image pickup device 20, it corresponds to being thesubject 32's radiation image that entered the image sensor.

As described above, since the dielectric multilayer film mirror 6 ofthis embodiment has a high reflectance, the scintillator panel 1 and theradiation image sensor 2 that use this dielectric multilayer film mirror6 are high in optical output.

In order to evaluate the sensitivity to radiation 30 and the corrosionresistance of the radiation image sensor 2 having the scintillator panel1 prepared in the above-described manner, three samples (referred torespectively as “Examples 1 to 3”) were prepared as examples of thisinvention and two samples (referred to respectively as “Prior-ArtExamples 1 and 2”) of the prior-art type radiation image sensors wereprepared with respectively different arrangements. Table 1 shows thearrangements of these samples.

TABLE 1 Arrangements of the compared samples Arrangement LightSeparation Sample Substrate reflecting film preventing layer Prior-ArtPyrex glass Aluminum film None Example 1 Prior-Art Amorphous Silver filmExample 2 carbon Example 1 Pyrex glass Example 2 Amorphous DielectricPolyimide carbon multilayer film Example 3 Aluminum plate

With each of the samples, CsI was used for the scintillator, apolyparaxylylene film was used as the protective film, and C-MOS wasused for the image pickup device.

As a test for evaluating the sensitivity with respect to radiation 30, afixed amount of radiation 30 was irradiated onto each of the samples andthe optical output values were measured. As a test for evaluating thecorrosion resistance, a shelf test over several days was conducted onjust the scintillator panels from which the image pick devices 20 hadbeen removed. The results of these tests are shown in Table 2. Theoptical output values are indicated as relative values with that of thePrior-Art Example 1 being set to 100%.

TABLE 2 Test Results of the Samples Test item Relative Sample outputvalue Corrosion resistance Prior-Art 100% The Al film corroded uponbeing left Example 1 for 1 to 2 days under 40° C. air temperature and90% humidity. Prior-Art 140% The Ag film corroded upon being leftExample 2 for 1 to 2 days under room temperature and room humidity.Example 1 140% No changes. Example 2 130% No changes. Example 3 135% Nochanges.

Each of the Examples 1 to 3 were higher in optical output value than thePrior-Art Example 1 in which an aluminum film is used as the lightreflecting film and was approximately equal in optical output value tothe Prior-Art Example 2 in which a silver film is used. With regard tothe corrosion resistance test, whereas corrosion occurred in 1 to 2 dayswith the Prior-Art Examples 1 and 2 that use metal films, changes werenot seen with the Examples 1 to 3 that use dielectric multilayer filmmirrors 6.

Also, the following test was conducted in order to check the effects ofseparation preventing layer 7. As samples, ten Pyrex glass (PX)substrates of 50 mm square and 1 mm thickness, each having 27 layers ofthe dielectric multilayer film mirror laminated thereon, were prepared.From each of these samples, five samples with polyimide layer 7 beingcoated onto the dielectric multilayer film mirror 6 as the separationpreventing layer and five samples without coating were prepared, andwith all samples, scintillator CsI was deposited. With each sample, tenlayers of CsI were deposited, and the thickness was varied in fivestages. The number of samples for which the separation of CsI occurredwas examined.

TABLE 3 Occurrence of separation of CsI with respect to thickness of CsIand existence of polyimide layer Thickness of CsI 100 μm 200 μm 300 μm400 μm 500μm Without polyimide layer 0/10 0/10 0/10 3/10 8/10 Withpolyimide layer 0/10 0/10 0/10 0/10 0/10

As indicated clearly in Table 3, whereas in the case of samples that donot use the polyimide layer 7 on the dielectric multilayer film mirror6, separation began to occur at the point at which the thickness of theCsI exceeded 400 μm, separation of CsI was not seen with samples usingthe polyimide layer 7. This test also showed that in a case where thescintillator 10 is doped with T1 in the form of CaI (T1) or NaI(T1), thepolyimide layer 7 simultaneously prevents the problem that the T1diffuses slightly into and colors the dielectric multilayer film mirror6 in the process of forming the scintillator by vapor deposition.

The above test results confirm that this embodiment's scintillator panel1 and radiation image sensor 2 output a high optical output, areexcellent in corrosion resistance, and also exhibit the effect ofprevention of separation of the scintillator.

Other embodiments of this invention's scintillator panel and radiationimage sensor now be described in detail.

FIG. 5 is a longitudinal sectional view, showing a second embodiment ofa scintillator panel according to the present invention. Thisscintillator panel 1 a has nearly the same arrangement as thescintillator panel 1 of the first embodiment shown in FIG. 1. Thedifferences are that a dielectric multilayer film mirror 6 a, formed bylaminating Ta₂O₅/SiO₂, which has a high reflectance for light from thevisible light to the ultraviolet range, is used and a so-calledphotostimulable phosphor of CsBr : Eu, etc., is used as scintillator 10a.

Unlike the scintillator panel 1 shown in FIG. 1, this scintillator panel1 a is used by irradiating radiation 30 from the scintillator 10 a side.The scintillator 10 a is excited by the radiation that enters in such amanner. Thereafter, by scanned illumination of a He-Ne laser beam 34across the scintillator 10 a as shown in FIG. 6, light that is inaccordance with the amount of the irradiated radiation 30 is emittedfrom the scintillator 10 a. This emitted light is detected by lightdetector 22 and converted into electrical signals to enable theacquisition of image signals corresponding to the radiation image.

By thus using a photostimulable phosphor for scintillator 6 a, storingthe radiation image temporarily, and reading out the image by laser beamscanning, the need to prepare an image pickup device of larger area iseliminated and the acquisition of a large-area radiation image, such asan image obtained for chest imaging, etc., is facilitated. Besides theabovementioned CsBr : Eu, various phosphors, such as those disclosed inJP No. 3,130,633, may be used as the photostimulable phosphor. Also, theTiO₂/SiO₂ laminate used in the first embodiment or an HFO₂/SiO₂laminate, etc., may be used for the dielectric multilayer film mirror.

FIG. 7 is a longitudinal sectional view, showing a second embodiment ofa radiation image sensor according to the present invention. With thisradiation image sensor 2 a, the radiation image sensor 2 shown in FIG. 3is provided furthermore with a housing 25 that covers the entirety ofscintillator panel 1. This housing 25 is made of a material, forexample, black polycarbonate, which has a radiation transmittingproperty, protects the entirety, and blocks external light. Light thathas been emitted by the scintillator 10 and has been transmitted throughthe dielectric multilayer film mirror 6 and the Pyrex glass substrate 5is thus absorbed by the housing 25 to restrain the light from returningto a position that differs from the scintillator 10 side position fromwhich the light was emitted and thereby restrain the degradation ofresolution due to such stray light. The entry of extraneous light thatacts as noise from the exterior can also be restrained and a high S/Nratio can be maintained.

Also, this housing 25 is provided in a condition where it is put inpress-contact against the Pyrex glass substrate 5 of the scintillatorpanel 1, and the scintillator panel 1 is adhered closely to the imagepickup device 20 by this press-contacting action. The occurrence ofleakage of light, cross-talk, etc., in the process of recognizing thelight emitted by the scintillator 10 by the image pickup device 20 canthereby be prevented. In order to realize an even higher degree ofadhesion, a sponge or other elastic material may also be placed betweenthe Pyrex glass substrate 5 and the housing 25.

As mentioned above, the use of glass as the substrate of thescintillator panel 1 provides the advantage of enabling the forming of ascintillator panel that is thin and yet will not bend. The use of adielectric multilayer film as a light reflecting film provides theadvantage of enabling the forming of a light reflecting film withexcellent corrosion resistance and high reflectance. Though when ascintillator panel that incorporates both of these is formed,transmitted light, which causes lowering of contrast, will occur, withthe present embodiment, this transmitted light is absorbed by theprovision of the housing 25 which has a light absorbing property,thereby enabling the advantages of the two abovementioned components tobe put to use while resolving the problem that occurs when the twocomponents are used.

FIG. 6 is a longitudinal sectional view, showing a third embodiment of aradiation image sensor according to the present invention. With thisembodiment (radiation image sensor 2 b), an image pickup device 20 isfixed on a sensor substrate 22, on which driving and reading circuitsare mounted, the image pickup device 20 is fixed in adhesion with ascintillator panel 1 by the fixing of the scintillator panel 1 onto thesensor substrate 22 by fixing jigs 23, and the entirety is covered by ahousing 25 made of black polycarbonate. Since the scintillator panel 1is adhered closely to the image pickup device 20 by the cooperativeaction of the fixing jigs 23 and the housing 25 a, the occurrence ofleakage of light, cross-talk, etc., in the process of recognizing thelight emitted by the scintillator 10 by the image pickup device 20 canbe prevented. Though in the Figure, there is a space between the glasssubstrate 5 and the housing 25 a, these components may adhered together.By this structure, the occurrence of light, which, upon transmissionthrough the Pyrex glass substrate 5, is reflected inside housing 25 andre-enters the Pyrex glass substrate 5 to give rise to the lowering ofcontrast and other degrading effects on the optical output, can berestrained and the lowering of the resolution and the S/N ratio can berestrained.

With regard to the housings 25 and 25 a, in addition to making thehousing itself from a light-absorbing member, the inner surface thatcontacts the Pyrex glass substrate 5 may be subject to matte furnishing,coating of a light-absorbing coat, or adhesion of a light-absorbingmember.

In order to evaluate the contrast ratio of a radiation image sensor withsuch a housing, a sample (referred to as “Example A”) of thisinvention's embodiment and a sample (referred to as “Comparative ExampleB”) of a prior-art type radiation image sensor were prepared as mutuallydifferent arrangements. Besides having or not having a housing, ExampleA and Comparative Example B are made the same in arrangement and withboth, a dielectric multilayer film mirror is formed on Pyrex glass, ascintillator of CsI is disposed on the film mirror, a polyparaxylylenefilm is used as the protective film, and a C-MOS type image pickupdevice is used as the image pickup device.

As a test for measuring the contrast ratio, radiation was irradiatedupon placing a lead object of 3 cm diameter and 0.5 mm thickness on thehousing, the signal values acquired by the radiation image sensor for aportion covered by the lead and for a portion exposed to radiation,respectively, were measured, and the ratio of these values was computed.As a result, in comparison to the Comparative Example B, the contrastwas improved by 10% and a clearer image was acquired with the Example A.

The abovementioned test results thus confirmed that this embodiment'sradiation image sensor enables the acquisition of images with sharpcontrast.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

INDUSTRIAL APPLICABILITY

The scintillator panel and radiation image sensor according to thepresent invention can be used favorably for chest imaging and othermedical uses as well as for non-destructive inspection and otherindustrial applications.

1. A scintillator panel comprising: a heat-resistant substance; adielectric multilayer film mirror, deposited on said heat-resistantsubstrate; a scintillator, deposited so as to arrange a plurality ofcolumnar structures on said dielectric multilayer film mirror andconverting incident radiation into light and emitting this light; and aprotective film, covering at least said scintillator; wherein saiddielectric multilayer film mirror reflects light emitted from saidscintillator and returns this light toward said scintillator, and saidscintillator panel further comprising: a separation preventing layer,which prevents the separation of said scintillator from said dielectricmultilayer film mirror, disposed between said dielectric multilayer filmmirror and said scintillator.
 2. A scintillator panel comprising: aradiation transmitting substrate with heat resistance; a dielectricmultilayer film mirror, formed on said radiation transmitting substrate;a scintillator, deposited so as to arrange a plurality of columnarstructures on said dielectric multilayer film mirror and convertingradiation, which as entered said radiation transmitting substrate andhas passed through said dielectric multilayer film mirror, into lightand emitting this light; and a protective film, covering at least saidscintillator; wherein said dielectric multilayer film mirror reflectslight emitted from said scintillator and returns this light toward saidscintillator, and said scintillator panel further comprising: aseparation preventing layer, which prevents the separation of saidscintillator from said dielectric multilayer film mirror, disposedbetween said dielectric multilayer film mirror and said scintillator. 3.The scintillator panel according to claim 1 or 2, wherein saidscintillator has CsI or NaI as the main component.
 4. The scintillatorpanel according to claim 1, wherein the scintillator is aphotostimulable phosphor.
 5. The scintillator panel according to any ofclaims 1 to 2, wherein said protective film is an organic film.
 6. Thescintillator panel according to any of the claims 1 to 2, wherein saiddielectric multilayer film mirror is a multilayer film having laminatedstructure with alternating TiO₂ or Ta₂O₅ and SiO₂ layers.
 7. Thescintillator panel according to any of claims 1 to 2, wherein theseparation preventing layer is a polyimide layer.
 8. A radiation imagesensor comprising: the scintillator panel according to any of claims 1to 2; and an image pickup device, disposed so as to face saidscintillator panel and converting the light emitted by said scintillatorto electrical signals.
 9. The radiation image sensor according to claim8, further comprising a light-absorbing housing that covers saidscintillator panel.
 10. The radiation image sensor according to claim 9,wherein said housing is made of polycarbonate.
 11. The radiation imagesensor according to claim 9, wherein the inner surface of said housingis matte finished.
 12. The radiation image sensor according to claim 9,further comprising a fixing jigs that fix the scintillator panel inadhesion with said image pickup device.
 13. A method for making ascintillator panel comprising the steps of: preparing a heat-resistantsubstrate; repeatedly depositing a dielectric film of desired thicknessonto said substrate to form a dielectric multilayer film mirror withpredetermined reflection characteristics; forming a separationpreventing layer for preventing a separation of a scintillator which isformed by subsequent step; depositing columnar structures ofscintillator on said separation preventing layer; and coating thescintillator with a protective film.
 14. A method for making a radiationimage sensor comprising the step of positioning an image pickup deviceso as to face the scintillator subsequent the steps of claim
 13. 15. Themethod for making the radiation image sensor according to claim 14,further comprising the step of covering the scintillator panel with alight-absorbing housing subsequent the steps of claim 14.